Rheumatoid arthritis is a chronic inflammatory arthritis that afflicts approximately 1% of adults (Mitchell, D. 1985. Rheumatoid Arthritis. P D Utsinger, N J Zvaifler, G E Ehrlich, eds. J.B. Lippincott Co., Philadelphia, pp. 133-150). The distribution of affected joints is symmetric and typically involves the small articulations of the hands and feet, although the larger appendicular joints like the shoulders and hips are often affected in established disease. Joint deformities, including ulnar deviation of the metacarpal phalangeal joints of the hand or destruction of the weight bearing joints, can occur late in the disease.
The symptoms of the disease result from a massive increase in the number of cells lining the synovium of the joint. The various cell types which are present include type A synoviocytes, which have the characteristics of monocytes or terminally differentiated macrophages, and type B synoviocytes which are fibroblast-like. As these cells increase in number, the continuous inflammation causes initial symptoms. Eventually, local release of enzymes by the synovial internal lining degrade the extracellular matrix and cause deformity.
The mainstays of therapy for rheumatoid arthritis include non-steroidal anti-inflammatory drugs, injectable gold salts, immunosuppressive agents, and methotrexate. While controlled studies do show some clinical benefit from these drugs, improvement is often limited and toxicity is common. Furthermore, most data suggest that these agents do not halt the rate of cartilage or bone destruction. Hence, a novel treatment that is directed at the pathogenesis of the disease with potential disease modifying activity would be a major improvement. The origin of the cells in the hyperplastic synovial lining in chronic inflammatory joint diseases remains controversial.
Necrosis and apoptosis are two basic processes by which cells may die. In necrosis cell death usually is a result of cell injury. The cells tend to swell and lyse, and the cell contents ultimately spill into the extracellular space. By contrast, apoptosis is a mode of cell death in which single cells are deleted in the midst of living tissues. Apoptosis accounts for most of the programmed cell death (PCD) in tissue remodeling and for the cell loss that accompanies atrophy of adult tissues following withdrawal of endocrine and other growth stimuli. In addition, apoptosis is believed to be responsible for the physiologic death of cells in the course of normal tissue turnover (i.e., tissue homeostasis) (Kerr, J. F., et al, 1972. Br. J Cancer 26: 239-257; Wyllie, A. H., et al. 1980. Int. Rev. Cytol. 68: 251-306).
The effector mechanisms of apoptosis are only incompletely understood, but the nuclear changes which occur appear to be caused by the activation of endogenous calcium-magnesium-sensitive nucleases that cleave chromatin between nucleosomes and reduce the DNA of apoptotic cells. A number of regulators of apoptosis have been identified. Some of these are already familiar as protooncogenes and oncosuppressor genes, including c-myc, bcl-2, p53, and ras. The protooncogene products and oncosuppressor proteins are believed to control cellular susceptibility to apoptosis (Isaacs, J. T. 1994. Curr. Opin. Oncol 6: 82-89). C-myc seems to determine whether cells continuously proliferate or enter apoptosis, depending on the availability of critical growth factors (Bisonnette, R. P., et al. 1994. In Apoptosis II: The Molecular Basis of Apoptosis in Disease. Cold Spring Harbor Laboratory Press). In cultured cells, expansion is usually determined by the presence of c-myc and growth factors, whereas apoptosis is seen when c-myc is present but growth factors are absent. Certain other oncogenes (e.g., ras and bcl-2) rescue cells from susceptibility to apoptosis. The oncosuppressor gene p53 is believed to initiate apoptosis by causing temporary G1/S arrest in cells expressing c-myc (Yonish-Rouach, et al. Mol. Cell Biol. 13: 1415-1423.).